1. Field of the Invention:
This invention relates to a material for forming electric contacts which are used in connectors, switches, relays or the like for electronic equipment and which are inexpensive and have high conductivity and springiness which could not be achieved by nowadays widely used copper alloys such as phosphor bronze.
2. Description of the Prior Art:
In these days, there is generally a tendency for articles or goods substantially in all fields to become lighter, thinner, shorter and smaller to fulfill the requirements in the present age in view of economy and saving of resources. Particularly in the field of electronic products, manufacturers endeavor to make small-sized and high-performance products. In order to fulfill the requirements, it is essential to realize the miniaturization of parts which include contacts such as connectors, switches and the like, a great number of which are used in the electronic equipment. Such miniaturization enables these parts to be utilized in electronic appliances in highly compact manner. However, it is almost impossible for the contacts made of prior art copper alloys to be miniaturized to any great extent.
More specifically, the contacts for use in connectors, switches and the like are required to be both highly conductive and springy. In general, however, metals having higher conductivity tend to exhibit lower springiness, while metals having higher springiness tend to exhibit lower conductivity. There has been no metal found which fulfills these two requirements, that is, the high conductivity and springiness simultaneously.
Therefore, as a least of evils, copper alloys such as phosphor bronze are generally used. They fulfill the above requirements to a certain extent, though not satisfactorily. However, even such a copper alloy, which is generally recognized to be most suitable for this purpose, has a much lower conductivity than that of pure copper and silver. In order to obtain contacts of high conductivity having the required springiness, therefore, sectional areas of the contacts have been made large to improve their conductivity, so that the contacts unavoidably become large. Accordingly, the miniaturization of contacts is severly limited. Moreover, copper alloys to be used as spring materials are generally not only very expensive but also very troublesome in production processes, inasmuch as they require high accuracy heat treatment by precisely controlling temperature, time and atmosphere for accurate and quality manufacture. Contacts made of such alloys are naturally expensive.
In order to eliminate the above disadvantages, it has been attempted to join, or laminate, a very springy metal and a highly conductive metal by pressure welding, electrolytic process or vapor deposition to obtain contacts having high conductivity and springiness. However, the contacts thus obtained have the following disadvantages which have precluded their adoption for practical use. For example, with this method of directly joining the different metals, diffusion between them progresses over time to change compositions and conditions of the metals, so that the initial characteristics of the metals degrade. When a stainless steel is used as a spring material and is coated with silver, copper or gold for high conductivity, oxide films on the stainless steel for preventing its rust should be removed in order to ensure the proper coating of the conductive metal. Therefore, the superior corrosion-resistance of the stainless steel is lost and serious corrosion occurs when pin-holes, cracks or the like occur in the coating metal. Furthermore, the electrical potential of the stainless steel is quite different from that of the copper, silver or gold, so that there is a risk of electrochemically promoting the corrosion of the stainless.
Another disadvantage with this type of joined or laminated body is that the composite body sometimes tends to separate or break due to thermal stresses resulting from the difference in coefficient of thermal expansion of each of the materials.
It is therefore impossible for the contacts of the prior art to realize the necessary miniaturization and low cost while improving the performance. Moreover, it is almost impossible to realize the miniaturization and low cost of electronic appliances by very compactly arranging therein the prior art connectors or the like.